Tornadoes and twisters

Tornado and twister are different names for the same type of storm – a violently rotating column of air over land associated with a severe thunderstorm. Tornadoes range in diameter from metres to hundreds of metres and generally last from a few seconds up to half an hour. They have an intense updraught near their centre, capable of lifting heavy objects such as cars and trees and causing enormous damage.

Tornadoes are not uncommon in Australia. In New South Wales they typically occur in late spring and summer, but can occur at other times of the year.

Tropical cyclones, hurricanes and typhoons

In Australia we call these large-scale storms tropical cyclones. In the USA they talk of hurricanes and in Asia, typhoons. Cyclones form over warm tropical waters where the sea's surface temperature is above 26° Celsius. They are typically hundreds of kilometres in diameter and can last for many days, with maximum winds greater than 62 km/h, or for severe cyclones, greater than 116 km/h. Strong winds, heavy rain, flooding and storm surges can cause major damage.

The tropical cyclone season in northern Australia is normally between November and April, with most cyclones occurring from January to March.